Field of the Invention
The present invention relates to an image processing apparatus for processing an image of an object to be examined, an image processing method, and a program.
Description of the Related Art
A tomographic imaging apparatus for eye portions, such as an optical coherence tomographic imaging apparatus (referred to as OCT), can observe a state of the inside of a retina layer three-dimensionally. The tomographic imaging apparatus is useful in more accurately diagnosing diseases, and it has received attention in recent years. One example of OCT is time domain OCT (TD-OCT) using a combination of a light source having a board-band region and a Michelson interferometer. With this, information on the strength of a signal with respect to a position in a depth direction is obtainable by detecting interferential light of reference light and backward scattered light from an object to be examined, the object to which measurement light has been emitted in a measurement optical path, while moving a reference mirror in a reference optical path along the optical axis direction.
Because the interferential light is measured while the reference mirror is mechanically moved, it is difficult for the TD-OCT to obtain a tomographic image at high speeds. One known method for obtaining a tomographic image at higher speeds is spectral domain OCT (SD-OCT) as OCT that obtains an interferogram by a spectroscope using a broad-band light source. Another known example is swept source OCT (SS-OCT) employing the technique of measuring spectrum coherence by a single-channel photo detector by using a high-speed wavelength-sweeping light source.
There is high myopia in which degeneration of tissue at an ocular posterior pole increases the eye's axial length and it causes symptoms of a high degree of myopia. Traditionally, a doctor subjectively evaluates the shape of the ocular posterior pole to determine whether an eye to be examined has high myopia or not by using a tomographic image, a picture of the eye fundus. Thus the determination varies depending on the evaluator. An image processing apparatus for quantitatively measuring the shape of the ocular posterior pole (the degree of a curve of the retina) to reduce the variations in the determination is disclosed in Japanese Patent Laid-Open No. 2013-153884. Japanese Patent Laid-Open No. 2013-153884 discloses determination of whether an eye to be examined has symptoms of posterior staphyloma by comparison with a normal range in a statistical database in a biaxial map of a mean value of a curvature and a variance of the curvature.
Japanese Patent Laid-Open No. 2013-48696 discloses an image analysis apparatus for ophthalmological diseases. This image analysis apparatus automates and quantifies the analysis to minimize determination dependent on a subject of a radiologist in diagnosis using 3D voxel MRI images of a head portion, including an eyeball. It discloses a quantification by calculating the eye's axial length and the degree of asymmetry with respect to the eye axis as parameters for image analysis. It also discloses classification of the high myopia types based on the MRI.